1. Field of the Invention
This invention relates to electrosurgical instruments capable of selectively cutting tissue and coagulating blood.
In all surgical procedures, and particularly cardiac or major vascular procedures, hemostasis or the control of bleeding is of the utmost importance. Electrocautery is the principal method used in surgery to achieve hemostasis.
The electrosurgical device consists of three components. In the first component, high frequency electrical energy is generated in an Electrical Surgical Unit, often called a "Bovie" after one of the earliest brands.
The second component is the instrument held by the surgeon, and is often called a pencil. It contains an electrical switch, and is connected to the electrical surgical unit by a cord. The pencil also holds the blade.
During the operation, the blade, with a low charge, is touched to the bleeding vessel and the surrounding tissue and coagulation occurs. The protein, also called eschar, coagulates on the blade.
The blade, at a high charge, is also used for cutting. In this mode, the electric curent actually vaporizes the adjacent tissue, which serves to bake the buildup onto the blade.
Over the course of the operation this buildup interfers with the electrical qualities of the blade and the surgeon must interrupt the operation to scrape the blade on an abrasive surface. When sufficient damage has been done to the blade, a new blade must be substituted.
2. Description of the Prior Art
The conventional balde for an electrosurgical instrument today is made of stainless steel. A recognized problem with these blades is that blood and tissue, or eschar, tend to adhere to and carbonize on the blade. This requires the suregon to interrupt the procedure at frequent intervals to clean the blade.
U.S. Pat. No. 4,228,800, entitled Bipolar Electrosurgical Knife, inventor Howard F. Degler, Jr. et. al. discloses bipolar electrosurgical blade with a center electrode. The criteria for the structure for the center electrode is said to be stringent than those for the side electrodes. The center electrode must be both reasonably refractory and medically acceptable. The preferred metals are stainless steel or tantalum.
U.S. Pat. No. 3,768,482, entitled Surgical Cutting Instrument Having Electrically Heated Cutting Edge, inventor Robert F. Shaw discloses an electrosurgical blade of tantalum nitride or other metal with a positive temperature coefficient of resistance. The stated object is to maintain a constant high temperature, generally between 300-1,000 C.
U.S. Pat. No. 4,682,596, entitled Electrosurgical Catheter and Method For Vascular Applications, inventor Thomas O. Bales discloses a method and device for removing atheroscleric placque buildup in blood vessels. One version discloses a catheter with a stainless steel tip which is a monopolar electrode. The tip may alternatively be platinum or tantalum. This tip may include an ultra thin insulating layer, such as ceramic metal oxide for capacitively coupling electrical energy to tissue.
U.S. Pat. No. 4,333,467, entitled Nonstick Conductive Coating, inventor Joseph J. Domincone discloses a non-stick coating comprising a first layer of conductive material deposited on the substrate and covered by a layer of organic non-stick material such as silicone.
U.S. Pat. No. 4,719,914, entitled Electrosurgical Instrument, inventor Gerald W. Johnson discloses an instrument with an attached moveable vacuum hood. The purpose of the moveable hood is to remove the eschar buildup during the operation.
U.S. Pat. No. 4,563,691 entitled Electrosurgical Electrode, inventor Judy Lindstron, discloses a electrosurgical hooked blade of stainless steel covered by telfon for athroscopy.
U.S. Pat. No. 4,785,807, entitled Electrosurgical Knife, inventor G. Marsden Blanch discloses a stainless steel blade, covered with a primer, and then covered by teflon.
U.S. Pat. No. 4,440,178 entitled Implantable Electrode, inventor Adrien Bussard discloses a cardiac pacemaker electrode. The electrode body is a sintered metal covered with a coating having a higher electrical resistance. A variety of metals are mentioned as suitable including niobium.